Experimental soil studies to estimate the nitrate load of the groundwater in the water protection areas of the island Fohr

摘要

At the Island Fohr water protection areas were established in 1985 because of the rising values of nitrate in the groundwater of the waterworks since the beginning of the eighties. Even a voluntary limitation of the intensity of agricultural landuse and an increasing afforestation of low productivity regions since 1975 did not show any effect on the groundwater until 1990. The siols in the water protection areas were soil-mapped, and to evaluate the release of nitrate from the surface soil with the new formed groundwater an in situ-incubation experiment to evaluate the mineralisation of nitrogen was set over one year at five locations. Out of this results combined with a climatic water balance nitrate concentrations in the new formed groundwater were calculated which are similar to those of the groundwater of the waterworks. It is concluded that in the past 30 years the widespread "Plaggenboden" were overload with nitrogen. That means that the C/N relation was forced more tightly, and the nitrogen content of the upper soil was nearly doubled. That induces an increasing biological activity with rising rates of nitrogen mineralisation.